Biosolids Incineration

Synergetics used CFD modeling to accurately predict the temperature of combustion by-products in a biosolids multiple hearth furnace (MHF). The CFD modeling accounted for both the drying and devolatilization processes, as well as the combustion. Various applications worldwide use MHFs, including calcination, carbon activation/regeneration, and biosolids incineration.

 

Figure 1: Hot combustion gasses created by hearth two combustion.

Validating the model was critical to presenting the client with reliable predictions since performing CFD simulations of a MHF was a novel, untested approach. Synergetics validated the model by conducting an onsite data measurement campaign that coupled temperature and gas sensor readings at the furnace exit and stack, at the same time as lab tests on biosolids feed composition. The measurements provided accurate inputs for the model, and outputs to validate against. To consider the model valid, a target difference of 20% was set on hearth temperatures, and exit gas O₂, CO and CO₂ levels. The validation was performed under two sets of operating conditions, and strong agreement was observed, with all validated quantities well under the 20% criteria.

The next stage was to use the model to predict the impact of predicted future operational loads on the furnace, and identify potential future issues. Based on the model’s output, Synergetics provided design and operational recommendations aimed at reducing emissions and operating costs. Moreover, they simulated and assessed a wide range of proposed engineering changes to determine the optimal solution, mitigating the client’s risk of making costly capital changes without achieving the desired improvements in stability and emissions.

Figure 2: An animation demonstrating the rabble arms raking the cake and showing its motion.

 

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